Many types of linear and rotary shear valves are known. Generally, a shear valve comprises a stationary member having a flat surface, through which a single port is formed and connected to a supply or receiving fluid element. A moving member generally having a plurality of ports connected to individual fluid conduits engages the flat surface of the stationary member, generally through a number of sealing elements adjacent each individual port. The valve operates through sliding movement between the stationary and moving members to axially align one of the individual ports in the moving member with the port in the stationary member. Thus, by selectively moving the movable member, an individual port which it comprises can be aligned with the port in the stationary member to complete a fluidic path and flow fluid.
Shear valves generally suffer from a common problem relating to their ability to form a seal between the stationary and moving members. The sealing element positioned between the moving member and the stationary member must provide a leak free seal between the members even after a considerable amount of wear. This requires the face of the sealing element, which generally engages and slides against the surface of the stationary member, to maintain complete sealing engagement. If the surface on which the sealing element slides is adequately finished and adequate means of lubrication is provided to prevent significant wear of the sealing member, seal integrity can usually be easily maintained. However, many environments in which shear valves are used are contaminated with foreign materials and abrasives which significantly reduce the ability of the sealing element to maintain a leak proof seal.
For instance, when dirt, crystalline residues, or corrosives can adhere to or become embedded in the surface upon which the sealing element must slide, it can be easily understood that the increased wear which this may cause significantly reduces the life of the seal. This can easily lead to premature seal failure and leakage, which in turn can result in even more build-up of dirt, residues and corrosive materials.
Attempts to enclose the critical portions of the valve from the surrounding environment have been ineffective since leakage of fluids which the valve is transmitting can easily cause sufficient contamination to severely affect their life. Thus, sealing rings and enclosures alone have not been effective in significantly aiding performance of shear valves, particularly in environments where salts, oxides and corrosive agents are being directed by the valve.